SQLAlchemy equivalent of named scopes in ActiveRecord

Question

Is there an equivalent of AR's named scopes? Named scopes are basically filters, that can be wrapped in a method, and then chained.

Here's an example from http://archives.ryandaigle.com/articles/2008/8/20/named-scope-it-s-not-just-for-conditions-ya-know:

class Article < ActiveRecord::Base

  # Get all articles that have been published
  named_scope :published, :conditions => ['published = ?', true]

  # Get all articles that were created recently
  named_scope :recent, lambda { { :conditions => ['created_at >= ?', 1.week.ago] } }

end

# Get all recently created articles that have been published
Article.published.recent

Here's an example using Django ORM: http://furrybrains.com/2009/06/22/named-scopes-for-django/

Answer 1

SQLAlchemy has hybrid attributes, which you could use to build any sort of system:

from sqlalchemy.ext.hybrid import hybrid_property


class Article(Base):
    @hybrid_property
    def published(self):
        return self.is_published == True

    @hybrid_property
    def recent(self):
        # this relies on the date arithmetic of the target backend
        return datetime.now() - self.created_at >= datetime.timedelta(days=7)


articles = query(Article).filter(Article.published, Article.recent).all()